1. Technical Field
The present invention relates generally to telephone networks; and more particularly to the routing of calls within a telephone network when high usage routes and fixed tandem routes are overloaded or unavailable, such routing also employed in an advanced intelligent network that supports local number portability.
2. Related Art
The structure of modern telephone networks often includes a traffic network and a coupled signaling network The traffic network includes a plurality of switches interconnected by traffic handling trunks. Many of these switches serve as central office switches that couple to a plurality of terminals as well as to other of the plurality of switches. The signaling network interfaces with the traffic network to perform call routing and management functions.
In an example of the manner in which a telephone network services a call, a switch (origination switch) receives a request from a calling terminal that includes a Dialed Number, the calling terminal requesting that the call be completed to a called terminal (associated with the Dialed Number) coupled to another switch (destination switch). The origination switch initiates call set up by interacting with the signaling network and requesting that the call be set up and routed to the called terminal (associated with the Dialed Number). During call set up, the origination switch transmits the Dialed Number to the signaling network. A signaling network element (such as a Service Switching Point) then performs a table lookup using the Dialed Number to determine the identity of the destination switch to which the called terminal connects. Once the identity of the destination switch is determined, the signaling network element performs a table lookup to determine the high usage route upon which the call may be routed. Once the high usage route is determined, the signaling network element attempts to allocate a routing path on the high usage route for the call. If the allocation is successful, the signaling network element sets up the call between the origination switch and the destination switch. The destination switch then completes the call to the called terminal.
However, if the signaling network element is unable to allocate a routing path on the high usage route, it performs another table lookup to determine whether a fixed tandem route exists from the origination switch to the destination switch. If such a fixed tandem route exists, the signaling network element attempts to allocate a routing path along the fixed tandem route. If a routing path on such fixed tandem route cannot be allocated, the signaling network element attempts to find another fixed tandem route to use. If the signaling network element cannot allocate a routing path on any of the fixed tandem route(s) for the call, the signaling network element routes the call to a resource that sends a xe2x80x9cfast busyxe2x80x9d signal, or another message to the calling terminal to indicate that the call could not be busy due to traffic or outage problems. When such an operation occurs, customer satisfaction is reduced and revenue is likely lost. This problem is becoming more pronounced with the introduction of Competitive Local Exchange Carriers (CLECs) which tend to overload the Incumbent Local Exchange Carrier""s (ILEC""s) systems.
Additional problems are encountered as service providers introduce Local Number Portability (LNP) support into their telephone networks. Because LNP causes many assumptions made with prior call routing techniques to be false, LNP cannot be easily introduced into the prior routing techniques. Thus, the service providers are faced with the difficult decision of either introducing LNP and causing problems in operating the existing network or to not introduce LNP.
Thus, there exists a need in the art for a call routing operation that may be implemented in a telephone network that successfully routes as many calls as possible, does not overload system resources and may operate in conjunction with Local Number Portability.
Thus, to overcome the shortcomings of the prior systems, among other shortcomings, a telephone network constructed according to the present invention includes an Enhanced Call Routing (ECR) function that reroutes calls when the high usage route and fixed tandem routes are overloaded or otherwise unavailable. Further, the ECR function tracks the operation of the telephone network on the basis of origination switches and destination switches and provides temporary network rerouting during outages and unusual over loading situations. Further, the ECR function supports Local Number Portability (LNP) so that it may operate in those telephone networks that are designed and/or modified to support LNP.
The ECR function, as described herein, is implemented in a signaling network element that intercouples with the traffic network. Such a signaling network element may be a Service Switching Point (SSP) and/or a Service Control Point (SCP), depending upon the specific implementation. The particular operations provided by the ECR function may dictate that, in some signaling networks, some or all of the functions be installed upon a particular type of signaling element. However, in other installations and with other functions supported, the ECR function may be installed on various of the signaling network elements or on a combination of two or more signaling network elements.
In a first operation according to the present invention, a call setup request is received by a Service Switching Point (SSP) from an origination switch in the traffic network, the call setup request including a Dialed Number (DN) or Local Routing Number (LRN). The SSP then performs a table lookup using the DN or LRN to determine the identity of a destination switch. The SSP then attempts to route the call by allocate resources on a high usage route. If unsuccessful in the allocation on the high usage route, the SSP attempts to allocate resources on the fixed tandem route(s).
If both attempts are unsuccessful, the SSP sends a Network_Busy message to the STP/SCP supporting the ECR function. The ECR function then attempts to determine an alternate tandem route for the call. If successful, the ECR function directs the SSP to route the call along the alternate tandem route, the alternate tandem route either being via the telephone network or via an alternate telephone network coupled thereto. If not successful, the ECR directs the SSP to send the call to a resource for caller notification.
In another operation according to the present invention, the ECR function monitors the number of Network_Busy messages received for each originating switch/destination switch pair in the telephone network. Based upon the number of Network_Busy messages received and the frequency at which they are received, the ECR function may determine that a temporary rerouting of calls between the originating switch and destination switch is required. In such case, the ECR function attempts to determine alternate tandem route(s) that may service the calls. If successful, the ECR function directs the origination switch to reroute incoming calls intended for the destination switch via the alternate tandem route(s).
The ECR function of the present invention supports LNP by mapping both dialed numbers and local routing numbers to destination point codes. The destination point codes uniquely identify the switches within the traffic network. Further operations are then based upon the destination point. Thus, operation correctly handles the LNP numbers.
Moreover, other aspects of the present invention will become apparent with further reference to the drawings and specification which follow.